And I guess it would be bad to use Show, but make custom instances for the problematic types that did not loop?
Alan On 18 Mar 2017 9:44 pm, "Edward Z. Yang" <ezy...@mit.edu> wrote: > We can't add Show instances for these types because many types > below them, e.g., Type, are cyclic, and would result in infinite > output. > > Perhaps we can add a new type class which a) faithfully represents > the Haskell syntax, but b) can deal with cyclic data. I think that's > something people would like (extra compilation time not withstanding). > But it sounds annoying to do since the deriving mechanism is not going > to help you. > > Edward > > Excerpts from Tom Sydney Kerckhove's message of 2017-03-18 14:03:48 +0100: > > Dear GHC Devs, > > > > I am trying to use GHC as a library but I'm having a lot of trouble with > > understanding what everything means. > > Up to now, I have been able to figure out what to do by reading the > > sources, but it ocured to me that much of my struggles could have been > > mitigated if the relevant types had Show instances. > > > > I am specifically talking about the types concerning type checking. > > TypecheckedModule and everything below that. > > I am aware that most of the types have an Outputable instance, but > > there are two problems with that: > > > > - 'Outputting' a value requires DynFlags. (yes, I know about pprTrace) > > - These instances are not intended to show the internal structure of a > > value, but rather a 'human readable' representation of a value. > > > > My questions for you: > > > > - Is there a reason that there are no derived 'Show' instances for most > > types? > > - Would you accept a diff that adds these? > > > > Thank you for your time. > > > _______________________________________________ > ghc-devs mailing list > ghc-devs@haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs >
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